Method for biosolid disposal and methane generation

ABSTRACT

A method for the disposal of biosolids, the method comprising providing a supply of biosolids; selecting an introduction formation below a ground surface, the introduction formation comprising a natural gas formation in a gas accumulation zone; introducing the biosolids into the introduction formation at a pressure sufficient to create and maintain fractures within the selected introduction formation; and allowing degradation of the introduced biosolids.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/123,828 titled “Method for Biosolid Disposal and MethaneGeneration” filed Apr. 15, 2002, now U.S. Pat. No. 6,491,616 which is acontinuation of U.S. patent application Ser. No. 09/917,417 titled“Method for Biosolid Disposal and Methane Generation” filed Jul. 27,2001, now U.S. Pat. No. 6,409,650 B1, issued Jun. 25, 2002; which is acontinuation-in-part of U.S. patent application Ser. No. 09/620,085titled “Method for Biosolid Disposal and Methane Generation,” filed Jul.20, 2000, now U.S. Pat. No. 6,287,248, issued Sep. 11, 2001; and claimsthe benefit of U.S. provisional patent application No. 60/150,677 titled“Method for Municipal Waste Disposal and Recovery of Byproducts,” filedAug. 25, 1999; the contents of each of which are hereby incorporatedherein by reference in their entirety.

BACKGROUND

Over 10 million tons of biosolids from municipal sewage sludge aregenerated each year in the United States alone. The prevailing methodsfor the disposal of biosolids include the application of the biosolidsto surface land application, such as to crop land, range land orforests, composting and landfill disposal. Each of these methods isassociated with disadvantages.

For example, one disadvantage of the application of biosolids to surfacelands is the resistance of persons living in the area of the applicationbecause of concerns about nuisances such as odor and wind-blown dustfrom the site of application. Biosolids application to surface land andlandfills also creates risks for contamination of potable surface waterand groundwater.

Further, disadvantageous weather conditions can delay the application ofbiosolids to surface land, and trucking biosolids to the applicationsite creates pollution and nuisances. Additionally, the capacity for thedisposal of biosolids by application to surface lands and landfills islimited and the associated costs are generally high. Also, greenhousegasses, such as methane and carbon dioxide, are generated by thedecomposition of the biosolids and these gases are released into theatmosphere at the sites of surface land application and most landfills.

Therefore, there is a need for an additional method for the disposal ofbiosolids that provides less risk for environmental contamination.Additionally, there is a need for an additional method for the disposalof biosolids that is less expensive. Further, there is a need for anadditional method for the disposal of biosolids that does not permit therelease of carbon dioxide and other green house gases into theatmosphere. Also, there is a need for an additional method for thedisposal of biosolids that can produce usable byproducts from biosolids.

SUMMARY

According to one embodiment of the present invention, there is provideda method for the disposal of biosolids. The method comprises, first,providing a supply of biosolids. The introduction formation comprises anatural gas formation in a gas accumulation zone. Next, the biosolidsare introduced into the introduction formation at a pressure sufficientto create and maintain fractures within the selected introductionformation. Then, the introduced biosolids are allowed to degrade.

In a preferred embodiment, the supply of biosolids can be derived fromat least one source selected from the group consisting of municipalsewage waste, waste water treatment waste, animal waste,non-human-non-animal industrial waste and a combination of thepreceding. In another preferred embodiment, the introduction formationis at least about 100 meters below the ground surface. In a particularlypreferred embodiment, the introduction formation is from between about500 and about 3,000 meters below the ground surface.

In a preferred embodiment, the introduction formation has a temperatureand the temperature of the introduction formation is greater that about25° C. In another preferred embodiment, the introduction formation has aporosity greater than about 15%. In a particularly preferred embodiment,the introduction formation is separated from the ground surface by oneor more pairs of alternating layers of high permeability and lowpermeability.

In a preferred embodiment, the method further comprises monitoringpressure in the one or more than one of the alternating layers of highpermeability and low permeability above the introduction formationduring a time selected from the group consisting of before biosolidsintroduction, during biosolids introduction, after biosolidsintroduction and a combination of before biosolids introduction, duringbiosolids introduction and after biosolids introduction. In a preferredembodiment, at least one low permeability layer of the one or morealternating layers of high permeability and low permeability comprisesshale. In a particularly preferred embodiment, the one or more pairs ofalternating layers of high permeability and low permeability is at leastthree pairs of alternating layers of high permeability and lowpermeability.

In a preferred embodiment, the degeneration of the biosolids generates agas selected from the group consisting of carbon dioxide, sulfurdioxide, hydrogen sulfide and combinations of the preceding. In aparticularly preferred embodiment, the method further comprisesdecreasing the rate of the generated carbon dioxide, sulfur dioxide,hydrogen sulfide or combination of the preceding by performing an actionselected from the group consisting of blending at least one waste streamwith the provided biosolids, inoculating the biosolids with at least onespecies of bacteria, changing the temperature of the biosolids, changingthe salinity of the biosolids, adding at least one chemical to thebiosolids and a combination of the preceding.

In a preferred embodiment, the method further comprises creatingfractures within the introduction formation before injecting thebiosolids into the introduction formation. In another preferredembodiment, the method further comprises transporting the selectedbiosolids to an introduction site by pipe before injecting thebiosolids. In a particularly preferred embodiment, the method furthercomprises monitoring pressure in the introduction formation at a timeselected from the group consisting of before injecting the biosolidsinto the introduction formation, during the introduction of thebiosolids into the introduction formation, after injecting the biosolidsinto the introduction formation and a combination of the preceding.

In a preferred embodiment, the method further comprises increasing therate of degradation of the biosolids by performing an action selectedfrom the group consisting of blending at least one waste stream with theprovided biosolids, inoculating the biosolids with at least one speciesof bacteria, changing the temperature of the biosolids, changing thesalinity of the biosolids, adding at least one chemical to the biosolidsand a combination of the preceding. In another preferred embodiment, thechemical added to the biosolids is potassium. In a particularlypreferred embodiment, the method further comprises allowing methane tobe generated by the degradation of the introduced biosolids andrecovering methane generated by the degradation of the introducedbiosolids, after injecting the biosolids into the introductionformation. In a particularly preferred embodiment, the rate of methanegeneration is increased by performing an action selected from the groupconsisting of blending at least one waste stream with the providedbiosolids, inoculating the biosolids with at least one species ofbacteria, changing the temperature of the biosolids, changing thesalinity of the biosolids, adding at least one chemical to the biosolidsand a combination of the preceding. In another preferred embodiment, thechemical added to the biosolids is potassium.

In a preferred embodiment, the degradation of the biosolids generates agas selected from the group consisting of carbon dioxide, sulfurdioxide, hydrogen sulfide and combinations of the preceding, and wherethe method further comprises decreasing the rate of the generated carbondioxide, sulfur dioxide, hydrogen sulfide or combination of thepreceding by performing an action selected from the group consisting ofblending at least one waste stream with the provided biosolids,inoculating the biosolids with at least one species of bacteria,changing the temperature of the biosolids, changing the salinity of thebiosolids, adding at least one chemical to the biosolids and acombination of the preceding. In another preferred embodiment, thechemical added to the biosolids is potassium.

FIGURES

The features, aspects and advantages of the present invention willbecome better understood with regard to the following description,appended claims and accompanying figures where:

FIG. 1 is a schematic diagram of one embodiment of the method for thedisposal of biosolids according to the present invention.

DESCRIPTION

In one embodiment, the present invention is a method for the disposal ofsolids, such as biosolids, comprising injecting the biosolids into deepunderground formations. The introduced biosolids are then allowed toundergo biodegradation, using the natural geothermal heat in the deepsubsurface. Biodegradation produces carbon dioxide, sulfur dioxide,hydrogen sulfide, methane and other gases. The generated carbon dioxideis absorbed by formation waters because it is highly soluble in water,and more soluble than methane. The residue from the biodegradation is acarbon-rich solid material that becomes permanently sequestered in theunderground formation.

In a preferred embodiment, methane generated by the degrading biosolidsis removed for conversion into usable energy, or storage for subsequentuse. In another preferred embodiment, the rate of biodegradation isincreased or the rate of methane production is increased or the rate ofcarbon dioxide or other undesirable degradation products is decreased byaltering environmental conditions in the formation or by addingsubstances or bacteria, or by adjusting the biochemical properties ofthe biosolids that are introduced into the formation. The present methodprovides significant cost savings and environmental benefits overcurrent technologies for the disposal of biosolids.

As used in this disclosure, the term “biosolids” is defined as solidparticles of matter that are dominantly comprised of organic material byweight.

The method of the present invention will now be discussed in greaterdetail. First, a suitable supply of biosolids is provided. In apreferred embodiment, the biosolids have sufficient concentration ofbiodegradable organic matter to generate exploitable quantities ofmethane. It is not necessary that all the wastes be biodegradable oreven organic as other solid components of the introduced biosolids willbecome permanently entombed in the introduction formation.

In a preferred embodiment, the biosolids disposed of by the presentmethod will be derived from municipal sewage or waste water treatmentwastes, such as produced by a major metropolitan area. Municipal sewagewastes comprise human biowastes, household scraps, sanitary paperproducts and other biological components, as well as mineral matter andsmall amounts of chemical products, such as solvents, acids, alkaliesand heavy metals, introduced into the waste stream through the municipalsewer system such as solvents, acids, alkalies and heavy metals.

Another suitable source of the biosolids is animal wastes from siteswhere the animals are raised or housed. The animal wastes can be mixedwith other organic materials such as sawdust or straw, or it may bemixed with mineral wastes. Still other suitable sources of biosolids arepulp and paper mill sludges, waste oil products including greases andwaxes, and wastes which are rich in organic debris dredged from harborsor estuaries.

After providing a suitable supply of biosolids, a suitable undergroundformation, designated the “introduction formation” in this disclosure,is selected below a suitable ground surface introduction site.Preferably, the formation is a high porosity, high permeability sandformation, significantly below usable groundwater, if present. In aparticularly preferred embodiment, the porosity is greater than about15%. In a particularly preferred embodiment, the introduction formationis below any groundwater which could be removed for human use and belowmultiple, thick and clearly defined layers of alternating lowpermeability, fluid flow barriers and high permeability fluid absorptionzones. The high permeability layers will preferably be sand of highporosity. The low permeability layers will preferably comprise shalesand other rocks containing clay minerals that have absorptive capacity.In a preferred embodiment, there should be at least two alternatinglayers of high permeability and low permeability separating any usablegroundwater, if present, and the deeper introduction formation. In aparticularly preferred embodiment, there should be at least fivealternating layers of high permeability and low permeability separatingany usable groundwater, if present, and the deeper introductionformation.

The total available storage volume of an introduction formation can becalculated based on the approximate average thickness and area of theintroduction formation, the average porosity of the introductionformation and the mechanical compressibility of the introductionformation, as will be understood by those with skill in the art withreference to this disclosure.

In another preferred embodiment, the introduction formation will be atleast about 100 m below the ground surface. This depth is generally deepenough to insure that the introduced biosolids will be sequestered, evenwithout thick and clearly defined layers of alternating lowpermeability, fluid flow barriers and high permeability fluid absorptionzones specific, and deep enough to ensure that the introduced biosolidswill not pose a potential threat to the environment or to watersupplies, and near enough to the surface to allow biosolids introductionin a cost-effective manner. In a particularly preferred embodiment, theintroduction formation is between about 500 m and about 3000 m below theground surface.

The introduction site typically requires less than 10,000 m² of surfaceland, unlike the larger areas required for surface landfills. Further,use of the surface land itself according the present method is onlytemporary, and after the disposal activity is complete, the surface landcan be returned to other uses.

The introduction site and introduction formation for use in the presentmethod should be selected to additionally protect ground and oceanwaters by properly selecting an appropriate geological interval whichdoes not outcrop or interact with near surface formations. Geochemicalanalysis of formation fluids can be used to verify that particularintroduction formations contain only ancient fluids and are not incommunication with shallower water sources.

It is also preferred that the selected introduction formation haspre-existing natural gas because this implies that the introductionformation is overlain by a suitable methane accumulation zone and iscapped by an unfractured layer of relatively low permeability so as toinhibit further upward methane movement. This configuration allows foraccumulation of gases generated by degradation of the biosolids andremoval of the gases for use as a fuel.

It is further preferred that introduction sites selected for use withthe present method have existing gas collection and measurementinfrastructure, and long histories of contained introduction operations.For example, preferred introduction formations include oil and gastrapping anticlines which over geologic time have proven to becompletely isolated.

The overlying low permeability layers, when present, above the preferredintroduction formation provide a permeability barrier to upwardmigration, as can be evidenced by historical oil/water accumulations,where the oil migrates upward until it is impeded by a permeabilitybarrier. The at least one additional overlying high permeability layeracts as a fluid flow sink in the unlikely event of a well casing cementfailure or a breach of a low permeability layer.

For example, if the well casing cement fails or a low permeability layeris breached and fluid migrates above the low permeability layer, thehigh permeability layer immediately above absorbs the excess pressureand migrating fluid. Pressure will then decline slightly in theintroduction formation and increase in the overlying layer. Thesepressure changes and fluid migration can be identified by monitorslocated in both zones, and periodic wellbore tracer surveys. Furthergroundward migration of the waste material will not occur unless thesecond higher high permeability layer also becomes highly pressurized.For material to migrate upwards from the introduction formation, theprocess of breach and absorption in the layers above the introductionformation would have to be repeated for each set of high permeabilityand low permeability layers above the introduction formation.

As an example, a suitable underground formation for introduction ofbiosolids according to the present invention would be a 100 m thick,unconsolidated sandstone formation lying between 1000 m and 3000 m belowthe ground surface, where the sands are poorly sorted and range intexture from very fine to coarse grained. An approximately 300 mthickness low permeability formation material would be present in the1,000 m interval immediately above the introduction formation, which areinterbedded with high permeability formations providing additionalgeologic barriers and safety zones and which could be easily monitored.

The introduction formation would have been used as a gas storage fieldfor at least ten years, the geology of the area would be wellcharacterized and injectivity into the introduction formation would havebeen established. A nearby well would preferably be present which couldbe used as an observation well for monitoring purposes. Furtherpreferably, there would be no groundwater extraction wells in the areaand groundwater would be regularly and extensively monitored.

In another preferred embodiment, the present invention includes creatingand maintaining fractures within the selected introduction formation bythe introduction of the waste under high pressure, such as partingpressure, as will be understood by those with skill in the art withreference to this disclosure.

After selection of a suitable introduction formation and introductionsite, the introduction equipment and associated facilities are locatedin an area adjacent to the introduction site. Introduction equipmentpreferably occupies a surface area of 10,000 m² or less, with noadditional surface construction or road work required.

The preferred biosolids introduction apparatuses should beenvironmentally secure in the handling of waste material. Furtherpreferably, they should be able to screen waste streams on a continuousbasis to avoid introduction of any oversize material into the wellborethat could lead to blockage, as well as to monitor and registerintroduction parameters such as rate, total volumes, pressure, densityand temperature in real-time.

Suitable cased and perforated wells are prepared or existing wellsmodified and extended into the introduction formation, and into themethane accumulation zone if desired. All wells used in the presentmethod are designed to seal against fluid and gas migration and areperiodically tested to ensure that migration is not taking place. Thecapacity for each well is preferably in the range of 500 to 2000 m³ perday of biosolids. By selecting multiple deep introduction targets, andalternating between multiple wells and intervals, a single site canprovide large-scale biosolids management capacity for many years.

In a preferred embodiment, each well used in the present invention hasseveral layers of protection. An outer steel casing (called the surfacecasing) extends from the surface to the lowermost depth of any usablegroundwater. This steel casing is surrounded by cement. One or moreadditional steel casing strings (called the production casing) extendsfrom the surface to the depth of the selected introduction formation.This casing is also surrounded by cement.

The biosolids to be disposed are pumped down a steel tubing past apacker located at an appropriate depth, for example, a depth of about1,500 m to 2,000 m. Outside the tubing is an annular region filled withfluid. The pressure of this fluid will be constantly monitored toimmediately detect any leak in the tubing. If material introduced downthe tubing does leak into the annular region, the material is stillcontained within an outer steel casing, which is in turn surrounded by acement sheath.

After selection of a suitable introduction formation and preparation ofthe introduction site, the biosolids are transported to the introductionsite. The transport can be by road-based transport. In a preferredembodiment, however, the biosolids are transported by pipe from thesource directly to the introduction site, which is located as close tothe source of material as practical.

In a preferred embodiment, a biosolids mixture is designed to generatemethane efficiently under the conditions present in the selectedintroduction formation. This is accomplished by measuring the chemicaland biological properties of the available biosolids stream, thephysical conditions in the target stratum, and adjusting the physicaland chemical properties of the biosolids to achieve efficient methanegeneration.

After the biosolids are introduced into the introduction formation andlocked in by the natural stresses present in the introduction formationand the low permeability zones immediately above the introductionformation, the introduced material is allowed to undergo degradationunder anaerobic conditions. Given a solids mixture undergoing anaerobicdigestion, an estimate of degradation can be obtained from first orderkinetics:W=W ₀ e ^(−kt)  (1)where W=mass of volatile introduced solids that have not degraded aftertime t, W₀=mass of solids deposited, k=decay coefficient, and t=time. Ingeneral the value of k will depend on a variety of factors including pH,temperature, salinity, mixing amount, and to some extent theconcentration of solids. Typical values for the exponent k are on theorder of 10⁻³, yielding a value for W of between 40-60% degradation peryear. For continuous introduction, the amount of material remainingafter some time t is determined by integration of equation 1. The massof gas produced will in general be equal to the amount of volatileintroduced solids degraded and is typically composed mainly of methane(50-60%), carbon dioxide (30-40%), nitrogen, and hydrogen.

In addition to the mechanical protection provided by the introductionwell design, and the natural protection provided by the selection of anappropriate introduction formation with multiple overlying barrier andbuffer zones, the present method preferably includes a continuousreal-time recording and display of pressure response in the introductionzone, in the first overlying high permeability zone, as well as in thewellbore annulus, to ensure containment of biosolids in the introductionformation. Any breach or deviation from anticipated introductionbehavior will be noted while material is still far below thegroundwater, allowing immediate remedial action. Additional processmonitoring can include several types such as pressure recording andanalysis, temperature recordings, surface deformation measurements andanalysis, and microseismic monitoring, such as monitoring pressure inone or more than one of the alternating layers of high permeability andlow permeability above the introduction formation during a time selectedfrom the group consisting of before biosolids introduction, duringbiosolids introduction, after biosolids introduction and a combinationof before biosolids introduction, during biosolids introduction andafter biosolids introduction, as will be understood by those with skillin the art with reference to this disclosure. The monitoring ispreferably performed at several depths below the groundwater base.

Preferably, fluid introduction into the introduction formation isepisodic in order to facilitate the monitoring of formation behavior.Bottom-hole pressure in the introduction formation is preferablymonitored continuously during daily introduction and nightly shut-in.This pressure information is analyzed to evaluate changing formationflow and mechanical properties and injectivity, and to determineformation parting pressure and material containment, as will beunderstood by those with skill in the art with reference to thisdisclosure. Additional biosolids will not be introduced if pressure inthe introduction formation remains abnormally high. As will beunderstood by those with skill in the art, in order for fluid to migrateout of the introduction formation, a breach must occur and the pressurein the introduction formation must be higher than the pressure in anadjacent formation. In addition to the continuous pressure monitoringand analysis, the present method preferably includes shutting down theintroduction well periodically to perform extensive well tests, tracersurveys and introduction formation tests to evaluate well integrity andhydraulic isolation in the near wellbore area.

In another preferred embodiment, the present method includes recoveringthe methane generated from the degradation of the introduced biosolids.The methane can then be used as a clean fuel. Alternatively, the methaneproduced can be left underground as a stored supply of future energy.Recovery of the methane is preferably done by injecting the biosolidsinto an appropriate geologic formation with a trapping mechanism.Preferably, the biosolids are introduced downdip below the water-oil orwater-gas contact in a geologic formation. The generated methane andcarbon dioxide will then migrate upwards due to gravity segregation.

Methane and carbon dioxide produced by the degradation of biosolidsaccording to the present invention will percolate through formationwater where much of the carbon dioxide will be sequestered undergroundby dissolution in the saline formation water, and where the high qualitymethane will accumulate in the gas trap. The difference in sequestrationis due to the much higher solubility of carbon dioxide in water relativeto methane (a ratio of at least 10:1) at temperature and pressureconditions typical for deep geologic formations. Methane, in particular,is a potent greenhouse gas. By injecting biosolids into the deepsubsurface, gas release to the atmosphere is eliminated and carbon ispermanently sequestered in deep saline formations.

Recovered methane from deep introduction formations used according tothe present invention is of higher quality than that generated insurface digesters or from surface landfills for two reasons. First, bypercolating through formation waters in the introduction formation, thecarbon dioxide component of the generated gases will be significantlyabsorbed due to the much higher solubility of carbon dioxide relative tomethane. Second, the methane generated according to the presentinvention is at higher pressure than methane generated by surfacelandfills and requires less compression for storage or use.

As can be appreciated, once the introduction formation is filled and themethane extracted, if desired, the equipment used for introduction ofbiosolids and recovery of methane can be removed and the site abandoned.This returns the surface land to the condition it was in previously andleaves the site unimpaired.

In a preferred embodiment, the present method includes increasing therate of biodegradation of the introduced biosolids. This is done byaltering environmental conditions in the introduction formation or byadding substances or bacteria, or by adjusting the biochemicalproperties of the biosolids that are introduced into the formation, orby a combination of these actions, to optimize the biodegradationprocess. In another preferred embodiment, the present method includesdecreasing the rate of production of undesirable products such as carbondioxide, sulfur dioxide and hydrogen sulfide.

For example, the rate of biodegradation can be increased by adjustingthe temperature and salinity of the biosolids so that the resultingphysical properties of the biosolids in the subsurface provides anoptimum environment for biodegradation, given the species of bacteriapresent in the biosolids and native to the introduction formation. Inanother preferred embodiment, biodegradation rates can be increased byadding appropriate natural or genetically engineered bacteria to thebiosolids prior to introduction, or after introduction. The inoculationcan be used to increase the decomposition rate of the biosolids intomethane under the specific temperature and pressure conditions at theintroduction formation depth, or to inhibit the production ofundesirable decomposition products, such as carbon dioxide, sulfurdioxide and hydrogen sulfide. Further, nutrients and other chemical ororganic agents, such as those that alter acidity, pH, or oxidationpotential, Eh, can be added to the biosolids for the same purposes.

For example, bacteria that are relied upon to promote biodegradation ofthe introduced biosolids can have high potassium requirements. Extrinsicpotassium, such as soluble salt potassium chloride (KCl), can be addedto an introduced biosolids to promote bacterial growth.

In general, it is preferred that chemicals added to the introducedbiosolids be only weakly soluble in water or insoluble so that any addedchemical is not removed during the water expulsion that accompaniescompaction of the introduced material in the formation. A suitablesource of potassium for addition to the biosolids, therefore, would befinely ground potash feldspar which contains potassium that is slowlyliberated in situ under the influence of aqueous exposure, hightemperatures and bacterial action.

For example, biodegradation in an introduction formation can be limitedby the supply of phosphorous present in one introduced biosolids. Inorder to improve biodegradation, a second waste stream rich inphosphorous can be blended with the first waste stream or introducedseparately, either simultaneously or alternating with the firstbiosolids. For example, a waste source rich in phosphorous can come froma chemical plant or from phosphorus-rich gypsum wastes (“phospho-gyp”).

In another example, some waste streams contain sterile biosolids due totheir alkalinity, such as waste streams from paper productionfacilities. In order to promote bacterial degradation of the wastes, asecond waste stream which is acidic can be blended with the first streamto adjust the pH of the streams to promote bacterial degradation of theintroduced biosolids.

In yet another example, natural or genetically engineered bacteria canbe added to the introduced biosolids to improve degradation. In apreferred embodiment, the bacteria added are anaerobic species becauseof the low concentration of oxygen in the introduction formations usedin the present invention. In a particularly preferred embodiment, thebacteria are methanogenic.

Additionally, a plurality of biosolids having different compositions canbe blended together to maximize biosolid degradation in the introductionformation, or to maximize the rate and quantity of methane generation,or to decrease the rate and quantity of generation of less desirabledecomposition products such as carbon dioxide, sulfur dioxide orhydrogen sulfide. For example, a source of animal waste that is rich inorganic material can be blended with a source of waste materia such as apulp residue, sawdust from a plywood mill, thermally treated wastes, orother waste that is less rich in organic material, and that is alsosterile. The two waste streams are blended in the optimum proportions,as will be understood by those with skill in the art, with reference toknowledge of the in situ conditions at the introduction formation andwith reference to this disclosure.

The temperature in the introduction formations used in the presentinvention can vary from 25° C. (e.g., 1 km deep introduction formationin Montana, US) to 100° C. (3 km deep introduction formation inWest-Central California, US). However, suitable thermophilic bacteriacan be used with introduction formations having considerably highertemperatures. Pressure also varies at the introduction formation depthsanticipated by the present invention, such as from about 10 MPA at adepth of 1 km depth to about 40 MPa at depths of between about 3 to 4km. Therefore, bacteria added to the biosolids must be chosen to besuitable to the temperature and pressures that will be encountered in aspecific introduction formation.

The method for the disposal of biosolids, according to the presentinvention, therefore, has several advantages over the currently usedtechniques. First, the present method reduces the potential and realimpact on surface waters and groundwater that can be associated withsurface application of biosolids, because the biosolids are introducedsignificantly below any usable source of groundwater. Second, thepresent method requires significantly less surface land area than landapplication for disposal of an equivalent volume of biosolids. Third,the present method does not permanently alter the surface land after thedisposal at the site is completed. Fourth, because the biosolids can bepumped to local sites for disposal, the present method significantlyreduces or eliminates truck traffic to distant disposal sites and,therefore, reduces the noise and environmental contamination associatedwith heavy truck traffic.

Fifth, the present method reduces the amount of methane and carbondioxide released into the atmosphere as compared to surface applicationof biosolids. Sixth, methane produced by the degradation of biosolidsaccording to the present method can be collected for use as an energysource. Seventh, biosolids disposal according to the present method canreduce the cost of biosolids management significantly compared withconventional surface application methods due to the reduced oreliminated need for trucking the biosolids to a distance site fordisposal.

Referring now to FIG. 1, there is shown a schematic diagram of oneembodiment of the method for the disposal of biosolids according to thepresent invention. A1 represents the surface facilities (storage,sizing, screening, mixing, blending, process monitoring and pumpingequipment) for the formulation of suitable biosolids mixtures forintroduction into an introduction formation.

A2 represents the introduction well (or one introduction well in anarray of introduction wells) that is cased and cemented in such a mannerso as to withstand the introduction pressures implemented over the lifeof the facility.

A3 represents the introduced biosolids that has been placed and hasrapidly, through excess water expulsion, become solidified by the greatweight of the overburden rocks. After all the methane possible has beengenerated by the biodegradation process, A3 becomes a dense andrelatively low permeability stratum that is rich in carbon and otherorganic molecules that were not biodegradable at the conditions in theintroduction formation. The sequestered carbon and other organicmolecules will not enter the atmosphere creating greenhouse effects.

A4 represents the introduction formation into which the biosolids, A3,was introduced. A4 is of sufficient porosity and permeability as toaccommodate the excess biosolids fluids without long-term pressurebuild-up or interaction with shallow, usable groundwaters. In general,the stratum A4 will be chosen as a laterally continuous stratum ofsufficient pore volume and flow path connectivity with adjacent stratato take all the water expelled from the biosolids during the compactionprocess.

A5 represents the evolution and upward movement path of the methanegenerated by the biodegradation process. Such movement occurs naturallybecause the methane is of a specific gravity that is far less than thatof any interstitial water, and therefore tends to rise through theporous medium, displacing liquid from the pores.

A6 represents the porous and permeable strata where the methane collectsthrough the upward migration and pore liquid displacement process, andfrom which strata the generated methane can be extracted for use. Thiszone, A6, is a “trap” for the evolved methane because of a suitablegeological structure, which can be in the form of structural closurewith folded beds that form an inverted bowl, as shown, or can be in theform of a change of rock type, not shown, in a combination of the two,or in some other suitable disposition of permeable and low-permeabilitystrata.

A7 represents the rocks overlying the introduction formation that are ofsufficiently low permeability that gas cannot flow upward through thepore space. Also, the overlying rocks A7 are non-fractured, or areminimally fractured so that the methane cannot escape to strata ofhigher elevation.

A8 represents one or more conventional gas wells that extract themethane from the accumulation site A6. The gas wells, A8, either existat the site before the disposal operation begins or are specificallyinstalled as cased, cemented wells, perforated so that the gas can flowinto the wellbore. Depending on the configuration of the strata, themethane extraction wells A8 may be vertical, horizontal or inclined.

A9 represents a surface facility for power generation that can use theextracted methane as a clean energy source. Alternately, the extractedmethane can be shipped directly to consumers for home use or industrialusers for other purposes.

Although the present invention has been discussed in considerable detailwith reference to certain preferred embodiments, other embodiments arepossible. For example, the method of the present invention can beapplied to the disposal of solids other than biosolids. Therefore, thescope of the appended claims should not be limited to the description ofpreferred embodiments contained in this disclosure.

1. A method for the disposal of biosolids, the method comprising: a)providing a supply of biosolids; b) selecting an introduction formationbelow a ground surface, the introduction formation comprising a naturalgas formation in a gas accumulation zone; c) introducing the biosolidsinto the introduction formation at a pressure sufficient to create andmaintain fractures within the selected introduction formation; and d)allowing degradation of the introduced biosolids.
 2. The method of claim1, where the supply of biosolids is derived from at least one sourceselected from the group consisting of municipal sewage waste, wastewater treatment waste, animal waste, non-human-non-animal industrialwaste and a combination of the preceding.
 3. The method of claim 1,where the introduction formation is at least about 100 meters below theground surface.
 4. The method of claim 1, where the introductionformation is from between about 500 and about 3,000 meters below theground surface.
 5. The method of claim 1, where the introductionformation has a temperature and the temperature of the introductionformation is greater that about 25° C.
 6. The method of claim 1, wherethe introduction formation has a porosity greater than about 15%.
 7. Themethod of claim 1, where the introduction formation is separated fromthe ground surface by one or more pairs of alternating layers of highpermeability and low permeability.
 8. The method of claim 7, furthercomprising monitoring pressure in the one or more than one of thealternating layers of high permeability and low permeability above theintroduction formation during a time selected from the group consistingof before biosolids introduction, during biosolids introduction, afterbiosolids introduction and a combination of before biosolidsintroduction, during biosolids introduction and after biosolidsintroduction.
 9. The method of claim 7, where at least one lowpermeability layer of the one or more alternating layers of highpermeability and low permeability comprises shale.
 10. The method ofclaim 7, where the one or more pairs of alternating layers of highpermeability and low permeability is at least three pairs of alternatinglayers of high permeability and low permeability.
 11. The method ofclaim 1, where allowing degradation of the biosolids generates a gasselected from the group consisting of carbon dioxide, sulfur dioxide,hydrogen sulfide and combinations of the preceding.
 12. The method ofclaim 11, further comprising decreasing the rate of the generated carbondioxide, sulfur dioxide, hydrogen sulfide or combination of thepreceding by performing an action selected from the group consisting ofblending at least one waste stream with the provided biosolids,inoculating the biosolids with at least one species of bacteria,changing the temperature of the biosolids, changing the salinity of thebiosolids, adding at least one chemical to the biosolids and acombination of the preceding.
 13. The method of claim 1, furthercomprising transporting the selected biosolids to an introduction siteby pipe before injecting the biosolids.
 14. The method of claim 1,further comprising monitoring pressure in the introduction formation ata time selected from the group consisting of before injecting thebiosolids into the introduction formation, during the introduction ofthe biosolids into the introduction formation, after injecting thebiosolids into the introduction formation and a combination of thepreceding.
 15. The method of claim 1, further comprising increasing therate of degradation of the biosolids by performing an action selectedfrom the group consisting of blending at least one waste stream with theprovided biosolids, inoculating the biosolids with at least one speciesof bacteria, changing the temperature of the biosolids, changing thesalinity of the biosolids, adding at least one chemical to the biosolidsand a combination of the preceding.
 16. The method of claim 15, wherethe chemical added to the biosolids is potassium.
 17. The method ofclaim 1, further comprising allowing methane to be generated by thedegradation of the introduced biosolids and recovering methane generatedby the degradation of the introduced biosolids, after injecting thebiosolids into the introduction formation.
 18. The method of claim 17,further comprising increasing the rate of methane generation byperforming an action selected from the group consisting of blending atleast one waste stream with the provided biosolids, inoculating thebiosolids with at least one species of bacteria, changing thetemperature of the biosolids, changing the salinity of the biosolids,adding at least one chemical to the biosolids and a combination of thepreceding.
 19. The method of claim 18, where the chemical added to thebiosolids is potassium.
 20. The method of claim 1, where the degradationof the biosolids generates a gas selected from the group consisting ofcarbon dioxide, sulfur dioxide, hydrogen sulfide and combinations of thepreceding, and where the method further comprises decreasing the rate ofthe generated carbon dioxide, sulfur dioxide, hydrogen sulfide orcombination of the preceding by performing an action selected from thegroup consisting of blending at least one waste stream with the providedbiosolids, inoculating the biosolids with at least one species ofbacteria, changing the temperature of the biosolids, changing thesalinity of the biosolids, adding at least one chemical to the biosolidsand a combination of the preceding.
 21. The method of claim 20, wherethe chemical added to the biosolids is potassium.